Intramolecular C-H oxidative addition to iridium(i) triggered by trimethyl phosphite in N, N'-diphosphanesilanediamine complexes

The reaction of Ir(SiNP)(cod)]PF6] (1]PF6]) and of IrCl(SiNP)(cod) (5) (SiNP = SiMe2{N(4-C6H4CH3)PPh2}2) with trimethyl phosphite affords the iridium(iii) derivatives of the formula IrHClx(SiNP-H){P(OMe)3}2-x](1-x)+ (x = 0, 3+; x = 1, 6) containing the ¿3C, P, P'-coordinated SiNP-H ligand (SiNP-H = Si(CH2)(CH3){N(4-C6H4CH3)PPh2}2). The thermally unstable pentacoordinated cation Ir(SiNP){P(OMe)3}(cod)]+ (2+) has been detected as an intermediate of the reaction and has been fully characterised in solution. Also, the mechanism of the C-H oxidative addition has been elucidated by DFT calculations showing that the square planar iridium(i) complexes of the formula IrClx(SiNP){P(OMe)3}2-x](1-x)+ (x = 0, 4+; x = 1, 7) should be firstly obtained from 2+ and finally should undergo the C-H oxidative addition to iridium(i) via a concerted intramolecular mechanism. The influence of the counterion of 2+ on the outcome of the C-H oxidative addition reaction has also been investigated

Divergent reactivity of 2-vinylpyridine and 1-vinylpyrazole in rhodium-phosphine systems: C-H activation and dinuclear chemistry

The Rh-I-Rh-III mixed valence dinuclear complex Rh-2-Cl-2(mu-H)(mu-eta(2),kappa(2)-C, N-NC5H4-2-(Z)CH=CH)( PPhMe2)(3) has been prepared by reaction of [Rh(mu-Cl)(eta(2)-coe)(2)](2) with 2-vinylpyridine in the presence of dimethylphenylphosphine as a result of C-H activation of the terminal olefinic proton. The X- ray structure presents anagostic Rh center dot center dot center dot HC and pi-pi interactions between aromatic rings. In contrast, 1-vinylpyrazole does not undergo a C-H activation process, resulting in the formation of dinuclear species supported by 1 vinylpyrazole bridges. Anagostic Rh center dot center dot center dot HC interactions and CH center dot center dot center dot Cl hydrogen bonds are responsible for the 3D packing of the complex. El complejo dinuclear de valencia mixta RhI-RhIII Rh2-Cl2(µ-H)(µ-¿2,¿2-C,N-NC5H4-2-(Z)CH=CH)(PPhMe2)3 ha sido preparado por reacción de [Rh(µ-Cl)(¿2-coe)2]2 con 2-vinilpiridina en presencia de dimetilfenilfosfina, como resultado de la activación C-H del protón terminal de la olefina. La estructura de rayos-X presenta enlaces anagósticos Rh···HC, así como interacciones p-p entre anillos aromáticos. Por otro lado, la reacción con 1-vinilpirazol no da lugar a una activación C-H sino que se observa la formación de una especie dinuclear soportada por ligandos 1-vinilpirazol puente. Diferentes interacciones anagósticas Rh···HC y de enlace de hidrógeno CH···Cl son responsables del empaquetamiento tridimensional del complejo

Hydroformylation of synthetic naphtha catalyzed by a dinuclear gem-dithiolato-bridged rhodium(I) complex

This work focuses on the use of a gem-dithiolato-bridged rhodium(I) Rh 2(µ-S 2CBn 2)(cod) 2 complex (cod = 1,5-cyclooctadiene, Bn 2CS 2 2- = 1,3-diphenyl-2,2-dithiolatopropane) dissolved in toluene in the presence of monodentate phosphite P-donor ligand (P(OPh) 3) under carbon monoxide/hydrogen (1:1, syngas) atmosphere as an effective catalyst for hydroformylation of some olefins (oxo-reactions). The capability of this system to catalyze the hydroformylation of hex-1-ene, cyclohexene, 2,3-dimethyl-but-1-ene and 2-methyl-pent-2-ene and their quaternary mixture (synthetic naphtha) has been demonstrated. This innovative method to perform the in situ hydroformylation of the olefins present in naphthas to oxygenated products would be a promissory work for a future industrial catalytic process applicable to gasoline improving based on oxo-reactions. An important observation is that variation of CO/H 2 pressure (6.8-34.0 atm), temperature (60-80 oC), reaction time (2-10 h), rhodium concentration ((1.0-1.8)x10 -3 mol/L) affect hydroformylation reaction rates. Optimal conversion to oxygenated products were achieved under Rh = 1.8 x10 -2 mol/L, P(CO/H 2) = 34 atm (CO/H 2 = 1:1) at 80 oC for 10 h

Preparation of Butadienylpyridines by Iridium-NHC-Catalyzed Alkyne Hydroalkenylation and Quinolizine Rearrangement

Iridium(I) N-heterocyclic carbene complexes of formula Ir(¿2O, O’-BHetA)(IPr)(¿2-coe) [BHetA=bis-heteroatomic acidato, acetylacetonate or acetate; IPr=1, 3-bis(2, 6-diisopropylphenyl)imidazolin-2-carbene; coe=cyclooctene] have been prepared by treating Ir(¿2O, O’-BHetA)(¿2-coe)2 complexes with IPr. These complexes react with 2-vinylpyridine to afford the hydrido-iridium(III)-alkenyl cyclometalated derivatives IrH(¿2O, O’-BHetA)(¿2N, C-C7H6N)(IPr) through the iridium(I) intermediate Ir(¿2O, O’-BHetA)(IPr)(¿2-C7H7N). The cyclometalated IrH(¿2O, O’-acac)(¿2N, C–C7H6N)(IPr) complex efficiently catalyzes the hydroalkenylation of aromatic and aliphatic terminal alkynes and enynes with 2-vinylpyridine to afford 2-(4R-butadienyl)pyridines with Z, E configuration as the major reaction products (yield up to 89 %). In addition, unprecedented (Z)-2-butadienyl-5R-pyridine derivatives have been obtained as minor reaction products (yield up to 21 %) from the elusive 1Z, 3gem-butadienyl hydroalkenylation products. These compounds undergo a thermal 6p-electrocyclization to afford bicyclic 4H-quinolizine derivatives that, under catalytic reaction conditions, tautomerize to 6H-quinolizine to afford the (Z)-2-(butadienyl)-5R-pyridine by a retro-electrocyclization reaction. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH Gmb

Synthesis of Titanium and Zirconium Complexes with 2-Pyridonate and 2, 6-Pyridinedithiolate Ligands

Treatment of complex Cp2TiCl2] with the lithium salt of 2-hydroxypyridine afforded complex Cp2Ti(Opy)2] (1), whereas the same synthetic strategy applied to the analogous zirconium compound Cp2ZrCl2] did not worked. However, the use of the metallocene Cptt 2ZrMe2] with protic ligands allowed directing the reactivity towards protonation of the methyl groups attached to zirconium. To check this approach we reacted Cptt 2ZrMe2] with methanol affording complex Cptt 2ZrMe(OMe)] (2), which was characterized in situ by NMR techniques. In the same line, the reaction of Cptt 2ZrMe2] with 2-hydroxypyridine gave complex Cptt 2Zr(Me)(Opy)] (3)//forcing the conditions of this reaction did not lead to the expected complex Cptt 2Zr(Opy)2], most probably due to the steric hindrance exerted by the bulky cyclopentadienyl ligands. Further reactions of complex 3 with ligands having acidic protons also led to the recovery of the starting complex. However, when shifting to the bifunctional ligand 2, 6-dimercaptopyridine py(SH)2] a double protonation of the methyl ligands in Cptt 2ZrMe2] occurred, allowing the isolation of mononuclear complex Cptt 2Zr(¿S, ¿S, ¿N-pyS2)] (4), upon evolution of methane. The molecular structure of complex 4 was determined by X-ray methods, showing the zirconium atom in a highly distorted trigonal bipyramidal arrangement//structural parameters indicate a conventional Zr-N bond, but rather weak Zr-S interactions

An insight into transfer hydrogenation reactions catalysed by iridium(iii) bis-n-heterocyclic carbenes

A variety of [M(L)2(L')2{kC,C'-bis(NHC)}]BF4 complexes (M = Rh or Ir; L = CH3CN or wingtip group; L' = I– or CF3COO–; NHC=N-heterocyclic carbene) have been tested as pre-catalysts for the transfer hydrogenation of ketones and imines. The conversions and TOF's obtained are closely related to the nature of the ligand system and metal centre, more strongly coordinating wingtip groups yielding more active and recyclable catalysts. Theoretical calculations at the DFT level support a classic stepwise metal-hydride pathway against the concerted Meerwein–Ponndorf–Verley (MPV) mechanism. The calculated catalytic cycle involves a series of ligand rearrangements due to the high trans effect of the carbene and hydrido ligands, which are more stable when situated in mutual cis positions. The reaction profiles obtained for the complexes featuring an iodide or a trifluoroacetate in one of the apical positions agree well with the relative activity observed for both catalysts

Mechanistic studies on the: N -alkylation of amines with alcohols catalysed by iridium(i) complexes with functionalised N-heterocyclic carbene ligands

Iridium(i) cyclooctadiene complexes featuring O- and N-donor functionalised NHC ligands efficiently catalyse the C-N coupling of amines with alcohols through a borrowing hydrogen mechanism. These catalysts have been applied for the N-alkylation of several aromatic and aliphatic primary amines with a range of alcohols including benzyl alcohol derivatives, straight-chain primary alcohols and secondary alcohols. The cationic complex [Ir(NCCH3)(cod){MeIm(2-methoxybenzyl)}]+ (cod = 1, 5-cyclooctadiene, MeIm = 3-methylimidazol-2-ylidene) having a rigid O-donor wingtip exhibits the best catalytic performance for the N-alkylation of aniline with benzyl alcohol giving a quantitative conversion to N-benzylaniline in 3 h. Experimental and theoretical studies at the DFT level on the N-alkylation of aniline with benzyl alcohol catalysed by the model compound [IrCl(cod)(IMe)] (IMe = 1, 3-dimethyl-imidazol-2-ylidene) support the participation of the iridium catalyst not only in the alcohol dehydrogenation and imine hydrogenation steps but also in the key step leading to the formation of the new C-N bond. Nucleophilic attack of an iridium-amido species generated in basic medium on the electrophilic aldehyde results in a hemiaminolate intermediate species from which the hemiaminal is released by alcoholysis. The free hemiaminal dehydrates to give the corresponding intermediate imine product that is hydrogenated by the iridium catalyst to the N-alkylated amine product. The iridium(i) complexes featuring functionalised NHC ligands are more active than [IrCl(cod)(IMe)] which highlights the positive influence of the functional group on the N-alkylation catalytic activity

Results from the CUORE-0 experiment

The CUORE-0 experiment searched for neutrinoless double beta decay in 130Te using an array of 52 tellurium dioxide crystals, operated as bolometers at a temperature of 10 mK. It took data in the Gran Sasso National Laboratory (Italy) since March 2013 to March 2015. We present the results of a search for neutrinoless double beta decay in 9.8 kg-years 130Te exposure that allowed us to set the most stringent limit to date on this half-life. The performance of the detector in terms of background and energy resolution is also reported

CUORE and CUORE-0 experiments

Neutrino oscillation experiments proved that neutrinos have mass and this enhanced the interest in neutrinoless double-beta decay (0vßß). The observation of this very rare hypothetical decay would prove the leptonic number violation and would give us indications about neutrinos mass hierarchy and absolute mass scale. CUORE (Cryogenic Underground Observatory for Rare Events) is an array of 988 crystals of TeO2, for a total sensitive mass of 741 kg. Its goal is the observation of 0vßß of 130Te. The crystals, placed into the a dilution cryostat, are operated as bolometers at a temperature close to 10 mK. CUORE commissioning phase has been concluded recently in Gran Sasso National Laboratory, Italy, and data taking is expected to start in spring 2017. If target background rate is reached (0.01counts/day/keV/kg), the sensibility of CUORE will be, in five years of data taking, T1/21026years (1? CL). In order to test the quality of materials and optimize the construction procedures, the collaboration realized CUORE-0, that took data from spring of 2013 to summer 2015. Here, after a brief description of CUORE, I report its commissioning status and CUORE-0 results